Molecular Resources for the Improvement of Tropical Ornamental and Fruit Crops
Location: Tropical Plant Genetic Resources and Disease Research
Title: Assaying for pollen drift from transgenic Rainbow to nontransgenic Kapoho papaya under commercial and experimental field conditions in Hawaii
Submitted to: Tropical Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2011
Publication Date: January 12, 2012
Citation: Gonsalves, D., Gonsalves, C., Carr, J., Tripathi, S., Matsumoto, T., Suzuki, J., Ferreira, S., Pitz, K. 2012. Assaying for pollen drift from transgenic Rainbow to nontransgenic Kapoho papaya under commercial and experimental field conditions in Hawaii. Tropical Plant Biol. 5(2):153-160. DOI:10.1007/s12042-011-9090-5.
Interpretive Summary: The transgenic Rainbow virus resistant papaya was released to growers in 1998 and saved the Hawaii papaya industry from devastation by papaya ringspot virus. However, in the early years after release of the transgenic papaya, Hawaii farmers still wanted to raise nontransgenic papaya to supply the lucrative Japan market and thus they continued to plant Rainbow and nontransgenic Kapoho in close proximity. Hawaii’s papaya industry only selects hemaphrodite trees for commercial production. Obtaining knowledge on the prevalence of transgene flow from Rainbow to Kapoho was especially important to seed producers who wanted to certify the purity of their seeds, and also to help nontransgenic papaya producers determine the potential that the Kapoho papaya would be fertilized by pollen from adjacent Rainbow fields. Our results showed very low levels (0.8%) of pollen flow from Rainbow to Kapoho in one plantation. The pollen flow was detected in the Kapoho papaya adjacent to the border of Rainbow. Transgene flow was not detected in four other plantations. However, controlled field plot experiments showed transgene flow from Rainbow to Kapoho occurred to a very high level (60%) to close-by female plants. This study will be of value to the papaya industry by helping growers, seed producers, and packers make informed decisions in locating their papaya plantations such if they do not want to have their nontransgenic papaya pollinated by transgenic pollen.
In 1992 papaya ringpsot virus (PRSV) was discovered in Puna district of Hawaii Island where 95% of the state of Hawaii’s papaya was being grown. By 1998 production in Puna had decreased 50% from 1998 levels. A PRSV-resistant transgenic papaya ‘Rainbow’ expressing the coat protein gene of PRSV was released commercially in Hawaii in 1998, and saved the papaya industry from further devastation. In the ensuing years since the release of the transgenic papaya, a number of farmers grew hemaphrodite nontrasngenic ‘Kapoho’ papaya in close proximity to plantings of hermaphrodite ‘Rainbow’ transgenic papaya. These plantings provided a unique opportunity to assay for transgenic-pollen drift under commercial conditions. Between 2004 and 2010, assay for the GUS (beta-glucoronidase) transgene in embryos were done to check transgenic-pollen drift in commercial ‘Kapoho’ plantings and in replicated field plots. Very low pollen drift (0.8%) was detected in fruit of Kapoho trees in the border row of one plantation when 90 embryos were assayed per fruit, while no pollen drift was detected in four other commercial plantings in which eight embryos were tested per fruit. Pollen drift averaged 1.3% of tested embryos in field plots where individual ‘Kapoho’ trees were immediately surrounded by two or four Rainbow trees. In contrast, 60.3% of tested embryos were GUS positive in similarly located female Kapoho trees. The very low transgene flow to close-by Kapoho plantings is likely due to the fact that hermaphrodite trees are used commercially in Hawaii and that these trees are largely self-pollinated before the stigma is exposed to external pollen.